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Einfluss verschiedener Prozessparameter auf die Temperaturentwicklung in der Umformzone beim Durchsetzen von Vergütungsstahl
Get PDFWährend der Kaltumformung von Blechwerkstoffen kommt es zu einem Temperaturanstieg in der Umformzone. Dieser resultiert neben Reibung hauptsächlich aus der Umwandlung plastischer Umformarbeit in Wärme. Die dabei auftretenden Temperaturen zeigen signifikante Auswirkungen auf den jeweiligen Fertigungsprozess, wie z.B. die Verschleißentwicklung des Werkzeuges oder das Umformverhalten des Blechwerkstoffes. Folglich ist die Kenntnis der auftretenden Temperaturen und deren Abhängigkeit von eingestellten Prozessparametern von hoher Bedeutung. Im Rahmen dieser Untersuchung wurde der Vergütungsstahl C45LC unter variierenden Prozessparametern durchgesetzt bzw. schergeschnitten. Aufgrund hoher Flächenpressungen und Umformgrade wurden diese Fertigungsverfahren verwendet, da hier hohe Temperaturen entstehen. Variiert wurden hierbei sowohl der Durchsetzspalt als auch die Stempelgeschwindigkeit. Die dabei entstehenden Temperaturen wurden während des Prozesses instantan mit einem Werkzeug-Werkstück-Thermoelement gemessen. Die Ergebnisse zeigen einen signifikanten Einfluss der Prozessparameter auf die ermittelten Temperaturen
Design and Experimental Evaluation of a Hybrid Wheeled-Leg Exploration Rover in the Context of Multi-Robot Systems
Get PDFWith this dissertation, the electromechanic design, implementation, locomotion control, and experimental evaluation of a novel type of hybrid wheeled-leg exploration rover are presented. The actively articulated suspension system of the rover is the basis for advanced locomotive capabilities of a mobile exploration robot. The developed locomotion control system abstracts the complex kinematics of the suspension system and provides platform control inputs usable by autonomous behaviors or human remote control. Design and control of the suspension system as well as experimentation with the resulting rover are in the focus of this thesis. The rover is part of a heterogeneous modular multi-robot exploration system with an aspired sample return mission to the lunar south pole or currently hard-to-access regions on Mars. The multi-robot system pursues a modular and reconfigurable design methodology. It combines heterogeneous robots with different locomotion capabilities for enhanced overall performance. Consequently, the design of the multi-robot system is presented as the frame of the rover developments. The requirements for the rover design originating from the deployment in a modular multi-robot system are accentuated and summarized in this thesis
Statistical glacier distribution in global- and regional-scale glacier modelling
Get PDFChanges in the total mass of glaciers globally form a major component of recent a and likely future a global mean sea-level rise (GMSLR), but only a handful of glaciers have detailed and long-term measurements that allow observational estimates of mass change on multi-decadal timescales. Estimating ice mass changes in glaciers on regional and global scales is typically handled with models that run on a per-glacier basis, using an inventory of glaciers collected using satellite mapping. This approach can result in mass change errors resulting from biases in the glacier inventories, particularly relating to small glaciers. The primary aims of this thesis are to improve our understanding of the distribution of glacierised area on large scales, and to use this information to inform improvements or corrections to regional- and global-scale glacier modelling efforts. Three papers are presented
Tourenplanung kooperierender Spediteure unter Aspekten des dynamischen Teilladungsverkehrs
Get PDFBoth collaborative and dynamic vehicle routing represent intensively studied problems of discrete mathematics. However, scientific studies on the combination of these two fields are rare. Aspects of dynamic collaborative vehicle routing using the example of less than truckload transportation are examined in this dissertation. Independent actors use an auction mechanism to exchange transportation orders among each other. At the beginning of a planning horizon not all transportation orders are known. That is why a rolling horizon planning is used to overcome this uncertainty. In order to ensure long-term cooperationa s aspects of the cooperative game theory are respected. Therefore, allocation mechanisms are integrated into a rolling horizon planning for the first time. In computational experiments developed algorithms are tested and the practical impact is evaluated
Effect of stress concentrations on the fatigue behaviour of structural adhesives
No full textAim of the present research is to investigate the effect of stress concentrations on the fatigue behaviour of structural adhesives using numerical and experimental approaches with focus on the prediction of fatigue lifetime of notched specimens. A model was proposed to explain the behaviour of SN curves of notched specimens in which the slope is controlled by the size of the highly stressed region and the stress concentration factor translates the position of the curve. The SN curves for crack initiation lifetime of both adhesives have indicated that most of the fatigue lifetime was spent on the crack initiation phase. A method for lifetime prediction based on the stress-life approach and the Theory of Critical Distances to account for the effects of stress concentrations on the fatigue lifetime was proposed. The critical distance length was obtained through a calibration. The effectiveness of the proposed method in predicting the fatigue lifetime of notched specimens was evidenced by the good accuracy obtained with regards to experimental results (relative error less than 12%) for different notched specimens and different structural adhesives
Der Einfluss der Datenkompetenz von Lehrkräften auf deren Akzeptanz von Vergleichsarbeiten und Potenziale interaktiver Rückmeldesysteme
Get PDFDieser Beitrag befasst sich mit der Rückmeldung von Ergebnissen aus Vergleichsarbeiten und geht der Frage nach, welche Rolle die Datenkompetenz von Lehrkräften und die grafische Gestaltung von Benutzerschnittstellen interaktiver Rückmeldesysteme bezüglich der Verständlichkeit von Rückmeldungen und der Akzeptanz von Lehrkräften gegenüber Vergleichsarbeiten spielen könnten. Aufgrund der hohen Komplexität der an Vergleichsarbeiten beteiligten Akteure und ihres kommunikativen Handelns, wird das Konzept der kommunikativen Figurationen von Hepp und Hasebrink (2014) herangezogen
Early rifting of Gondwana : Conclusions from the crustal structure of the Falkland Plateau
Get PDFDuring the Jurassic, the Falkland Plateau was part of Gondwana and occupied a position between the African, South American and Antarctic plates. Several contrasting kinematic models exist for the breakup of Gondwana because of the currently unknown crustal structure of the plateau. In this thesis, I present the results of recently acquired wide-angle seismic data along the entire plateau that provide sound constraints on its role in geodynamic reconstructions. The new data show that the Falkland Plateau Basin consists of up to 20 km thick oceanic crust. Maurice Ewing Bank is an up to 29 km thick continental fragment, which was directly attached to the Falkland Islands block during the Jurassic. Rifting between the Falkland Islands and the Maurice Ewing Bank started at 178 Ma and ceased at around 154 Ma
Untersuchung eines hybriden Brain-Computer Interfaces (BCIs) zur optimalen Auslegung als Mensch-Maschine-Schnittstelle
Get PDFPeople with partial or complete paralysis are usually dependent on nursing staff to cope with their daily activities. Alternatively, an assistance robotics system serves as a substitute for the lost motor skills and enables an improvement in the quality of life. With the help of a human-machine interface, the user can operate the system and initiate autonomous processes. If the system consists of a robot arm, the disabled person is able to grab and move objects. In the case of an error caused by the system, the user should be able to control the robot arm directly. With the interface developed in this work, a human being can open or close as well as move the robot gripper into any position and orientation. Since the target group of the system is people with very limited body movements, a Brain-Computer Interface (BCI) is used for communication. It establishes a communication channel between the human brain and the controlled robot arm. A special helmet is used for recording the brain signals, which, in addition to the measuring electrodes, has a stimulator in the peripheral field of vision of the user. This stimulator has four stimuli by which an evocation of event-related and visual potentials are provided. By detecting Steady State Visual Evoked Potentials (SSVEPs) and P300 potentials, the system can determine which stimulus the user has focused on. With this, four discrete commands are provided for the user to control the robot. For switching the stimulator on and off motor imaginations are used. A state machine with a control group for each translational and rotational movement is used to control the robot. A stepwise control, in which the gripper performs discrete steps, and a speed-based control, in which the movement of the gripper is started and stopped has been implemented. Switching between groups is performed by the sequential sending of two commands. In each group, the user can perform a movement in the positive and negative direction of the selected axis, change the step width or speed, and leave the group. Stopping at the target position and in dangerous situations occurs by closing the eyes and the thereby occurring artifacts and alpha waves in the signals. Both control concepts were tested in a study and evaluated with objective and subjective criteria. The experiments have shown that BCI-based robot arm control is feasible and useful
Towards an Advanced LISA Payload Architecture Featuring In-Field Pointing and Spherical Proof Masses
Get PDFThe prediction of gravitational waves in the early 20th century promised new means for observational astronomy, since they were expected to allow deeper insight into our universe. Recently, the first direct detection of gravitational waves by the earth based LIGO detectors - a major achievement along gravitational wave observation - confirmed the original prediction. This milestone elevated the interest in the development of enhanced as well as new detectors, which hopefully enable the discovery of new aspects of our universe. One of these new detectors is the planned Laser Interferometer Space Antenna (LISA) space mission, which will represent a giant interferometer for the observation of gravitational waves in space. LISA consists of three satellites, which are arranged in a triangular formation and form three interferometer arms. The detection will be performed via interferometric, inter-satellite laser distance metrology between free-flying proof masses, which act as the end points of the interferometer arms and will change their relative distances with respect to each other when a gravitational wave is passing. However, the strain amplitudes of gravitational waves are small and so will be the distance changes between the proof masses (in the order of a few tens of a picometer), which makes their detection very challenging. LISA will expand the currently available measurement bandwidth covered by the earth based detectors to lower frequencies, hence enabling the detection of new gravitational wave sources. In the baseline LISA payload architecture, changes in the angles of the triangular spacecraft formation, caused by the individual orbital mechanics of the spacecraft, are compensated by pointing of the whole telescope assemblies. This concept is called telescope pointing. During the LISA mission formulation study a new, alternative LISA payload architecture was developed and theoretically investigated. This concept features in-field pointing in order to compensate for these changes in spacecraft formation. The in-field pointing architecture offers potential savings in mass, volume and power consumption as well as potential improvements in measurement performance of the metrology instrument, compared to telescope pointing. Nonetheless, the technical realisation of the IFP concept in compliance with the requirements is highly demanding. This thesis covers two different and potentially limiting aspects concerning the realisation of an advanced LISA payload architecture including in-field pointing. The first one is part of the detailed investigations of the required wide-field telescope, suffering from mirror topography induced (optical) path length changes, so called piston, due to active beam steering and walking of the laser beam over the surfaces of subsequent telescope mirrors. This specific effect and its impact on the LISA measurement performance is investigated in more detail based on experimental measurements as well as a theoretical model. The second aspect investigated in this thesis is a novel concept for a LISA like inertial sensor, which features a spherical proof mass in combination with an all optical read-out. This concept represents an elegant solution for a low-noise, fully drag-free inertial sensor system, which could further increase the measurement performance of the LISA metrology instrument. In particular, the presented investigations include the development of a measurement setup for generating a detailed surface map of spherical proof masses, in order to calibrate its topography with respect to the sphere's centre of mass. First results of one-dimensional topography measurements of a SPM dummy are presented, representing a first step towards the generation of a complete two-dimensional surface map. Both topics are based on picometer-precision interferometric topography measurements, utilising highly sensitive heterodyne techniques. A major advantage of this measurement principle is its non-tactile nature, hence avoiding damage of the examined surfaces, while offering high levels of accuracy and reproducibility
Identität(en) tschechischer und slowakischer Skinheads in der Transformationszeit der CSSR / CR
Get PDFDer Beitrag beschäftigt sich mit der tschechoslowakischen und tschechischen Subkultur der Skinheads im Kontext der Transformationsprozesse der 1990er Jahre. Dabei analysiert er anhand der Framing-Methode die Konstitution des Neonationalismus dieses Jahrzehntes anhand der Skinhead-Bewegung. Die Skinheads werden dabei als agents eines gesamtgesellschaftlichen Rechtsrucks betrachtet. Exemplarisch erarbeitet der Beitrag anhand von Liedtexten einschlägiger Skinheadband sowie unter Betrachtung verschiedener Zeitschriftenartikel, die Angebote der Identitätskonstruktion der Subkultur und kontextualisiert sie im Hinblick auf den gesamtgesellschaftlichen Diskurs